Misc. Diagnostic tests/Statistics/PT and Sonographer Safety Flashcards
what is the gold standard in arterial evaluation
arteriography
describe how arteriography is performed
percutaneous puncture of an artery
catheter inserted and positioned into the vessel of interest
radiopaque contrast (dye) is injected into the vessel and is carried with the moving blood
fluoroscopy images the contrast and provides a picture of the lumen
catheter is removed, and the puncture site is controlled with manual pressure, pressure dressing or a vascular closure device
what are limitations for arteriography
contraindication due to contrast allergy or renal insufficiency - dye is cleared through the kidneys and may be nephrotoxic
given the lumen is viewed in two planes, the disease may be under or overestimated
what is magnetic resonance angiography (MRA)
employs a strong magnetic field and radio frequency energy to produce images in multiple planes
flowing blood is well distinguished from stationary soft tissues without contrast
what are limitations to magnetic resonance angiography
presence of pacemakers, metallic clips, and monitoring equipment can preclude its use
can overestimate disease due to either slow flow or turbulence
expensive
patients with claustrophobia may limit its use
what is a computerized tomography angiography (CTA)
employs ionizing radiation (x ray) to obtain cross sectional images of the soft tissue and blood vessels, especially good for aorta and peripheral arteries
IV contrast can provide a more detailed evaluation of some structures
wha are limitations to CTA
patient motion may blur the images
presence of pacemakers or metallic clips may result in shadows
limited application in small vessels
single plane use
expensive
significant ionizing radiation exposure
what is the gold standard for venous evaluation
duplex scanning
describe contrast venography
radiopaque dye or contrast injected into veins and x ray image depicts the vein lumen by showing the contrast
what are limitations to contrast venography
difficult technique and interpretation
expensive
invasive, carries a small risk of causing venous thrombosis
uncomfortable for patient
contraindication for patients with contrast allergies and severe PAD due to the risk of necrosis from contrast extravasation outside the vein into the tissues
what are the two types of venography techniques
ascending venography and descending venography
describe ascending venography
radioplaque contrast injected into a vein o nth dorsum of the foot
serial x rays are obtained as the contrast passes through the veins to identify filling defects, anatomic variations and collateral development
describe depending venography
evaluates retrograde flow resulting from valvular incompetence
patient in upright position
radiopaque is injected into the CFV
serial x rays obtained to determine if contrast flows retrograde down the leg
can determine the relative amount of reflux and location of incompetent valves
true positive
our test indicates disease (positive) and is correct (true)
true negative
our test indicates normal (negative) and is correct (true)
false positive
out test indicates disease (positive) and is incorrect (false)
false negative
our test indicates normal (negative) and is incorrect (false)
statistics rule
look at OUR test first to determine + or - and then at the gold standard to determine true or false
sensitivity
the ability of a test to detect disease when present
sensitivity = true positive / true positive + false negative
specificity
the ability of a test to identify normalcy (NO DISEASE PRESENT)
specificity = true negative / true negative + false positive
positive predictive value (PPV)
percentage of positive studies that are correct
PPV = true positive / true positive + false positive
negative predictive value (NPV)
percentage of negative studies that are correct
NPV = true negative / true negative + false negative
accuracy
percentage of ALL studies that are correct
accuracy = true positive + true negative / total number of exams
accuracy lies between
sensitivity and specificity
positive and negative predictive values
ex
sensitivity = 85%
specificity 90%
accuracy is 87% (lies in between)
positive predictive value 92%
negative predictive value 82%
accuracy is 87% (lies in between)
screening
likelihood of detecting these disorders at an early stage
testing
determine if disease is present or absent
SNOUT
sensitivity rules negative out
good for screening - you want a screening test to be highly sensitive, so you do not tell the person they do NOT have a disease, even if that meant picking up some false negatives
SPIN
specificity rules positive in
good for confirmatory testing - after you’ve identified all the positives by your highly sensitive screening test, you’d want a confirmatory test to be highly specific, so you do not tell the person they have disease when they do NOT
what is the grid for statistics
gold standard results always on top
study exam results always on the left
top row = positives
bottom row = negatives
A (true positive) / B (false positive)
C (false negative) / D (true negative)
the gold standard is the test that we compare our results to and is always assumed to be 100% correct
how to calculate sensitivity using grid
A / (A+C)
how to calculate specificity using grid
D / (D+B)
how to calculate PPV using grid
A / (A+B)
how to calculate NPV using grid
D / (D+C)
how to calculate overall accuracy using grid
A+D / (A+B+C+D)
NOT A CARD BUT A NOTE
do example on page 288
what is the rule of 30s
shoulder hyperabduction >30
scanning patient with body was index >30
duration (sonographer age >30 y/o or scanning >30 years)
